The pyrolytic treatment of scrap or waste automobile rubber tires has been extensively investigated particularly since the petroleum oil embargo in 1973. The prospect of obtaining useable oil from the tires has been a major focus of many researchers.
Such pyrolytic treatment of used tires involves the application of heat, generally ranging between 600.degree. F. and 1400.degree. F., in an oxygen-limited atmosphere. The products emulating from such pyrolytic treatment were (1) a combustible gas having a heating value of approximately 750 BTU per cubic foot, (2) a recovery oil having a gross heating value of 18,000 BTU per lb., and (3) carbon black (char). Generally the relative amounts of each product varied somewhat with temperature, pressure and detention time. Typical recovery ratios range from 5 to 20 percent gas, 20 to 50 percent oil, and 30 to 50 percent carbon black.
Typically the pyrolytic gas is burned to provide the heat energy for the pyrolytic process. Thus the economic feasibility centered principally on the commercialization of the pyrolytic oil and the carbon black rather than on the sale of the process gas.
The recovered rubber process oil had properties similar to No. 2 fuel oil and in many instances may be used in applications where No. 2 fuel oil is specified. Thus the commercial value of the recovered rubber process oil fluctuated with the price of No. 2 fuel oil. Furthermore it does not appear that the rubber process oil is acceptable for all heating oil applications. A detailed analysis of the rubber process oil reveals the presence of numerous chemicals which may be hazardous or toxic then burned causing unacceptable air contamination problems.
The carbon black obtained from pyrolysis can be used in a few applications as coloring in paints and dyes and coloring in low grade rubber products. Generally the carbon black contains as ash content of 10 percent with makes it unacceptable, without further rather expensive refining, for use in new tires. The new tire industry is the largest user of carbon black. Thus even the recovered carbon black has limited commercial value.
Consequently, despite the investment of large sums of money in research and development by both private and public organizations, the economic feasibility of the pyrolytic treatment of automobile rubber tires to obtain recyclable bi-products has yet to demonstrated.
Thus the vast majority of used rubber tires continue to be stockpiled in unattractive piles or disposed of in land fills or, if the demographics are favorable, burned as a primary or secondary fuel in an incinerator to produce electricity.
One of the objectives and advantages of this invention to be able to produce a valuable rubber process oil from used automobile rubber tires that is reusable as a petroleum based, rubber extender/plasticizing agent. These and other objects and advantages will become apparent upon reading the following description of a preferred embodiment of this invention.